Solar cell and a method for manufacturing the solar cell

ABSTRACT

The present invention relates to a solar cell and a method of producing the same. The solar cell comprises a porous light absorbing layer ( 1 ), a first porous conducting layer ( 2 ), a second conducting layer ( 3 ), a porous substrate ( 4 ) between the conducting layers, the porous substrate comprises a catalytic conducting portion ( 4   a ) in electrical contact with the second conducting layer and an insulating portion ( 4   b ) between the first porous conducting layer ( 2 ) and the conducting portion, and a conducting medium ( 5 ) for transporting charges between the conducting portion ( 4   a ) and the light absorbing layer ( 1 ). The conducting medium is located in the light absorbing layer ( 1 ), the first porous conducting layer ( 2 ), and partly the porous substrate ( 4 ) so that the insulating portion ( 4   b ) and a first part ( 4   a ′) of the conducting portion ( 4   a ) comprises the conducting medium and a second part ( 4   a ″) of the conducting portion is free of conducting medium.

TECHNICAL FIELD

The present invention relates to a solar cell. The present inventionalso relates to a method for manufacturing solar cells.

BACKGROUND

Dye-sensitized solar cells (DSC) are well known in the art, and work onsimilar principles as photosynthesis. Unlike silicon solar cells, thesecells obtain energy from sunlight using dyes, which can be manufacturedcheap and environmentally friendly.

A dye-sensitized solar cell has a light absorbing layer comprising aporous metal oxide, for example a few μm thick porous TiO₂ electrodelayer, dyed by adsorbing dye molecules and forming a working electrode.Sunlight is harvested by the dye, producing photo-excited electrons thatare injected into the conduction band of the metal oxide particles.Other words for dye in this context are chromophore, sensitizer andphotosensitizer.

There exists different types of dye-sensitized solar cells, such assandwich dye-sensitized solar cells and monolithic solar cells. Asandwich type dye-sensitized solar cell is normally manufactured bycombining two separately produced parts of a cell by laying one part ofthe cell over the other part. A sandwich type solar cell can comprise aTiO₂ electrode layer deposited onto a first transparent conductingsubstrate. The first transparent conducting substrate normally comprisesa transparent conducting oxide layer deposited onto a glass substrate.The transparent conducting oxide layer serves the function as anelectron collector extracting photo-generated electrons from the workingelectrode. The sandwich type dye-sensitized solar cell also has acounter electrode including a second transparent conducting substrateattached to the first transparent conducting substrate. The TiO₂electrode layer is in contact with an electrolyte and the secondtransparent conducting substrate.

Dye-sensitized solar cells of a monolithic type is, for example, knownfrom WO 2013/149787, WO 2013/149789, and WO 2014/184379.

FIG. 1a shows an example of a prior art monolithic dye-sensitized solarcell, known from for example U.S. Pat. No. 9,251,963, comprising aworking electrode including a light absorbing layer 1, a first porousconducting layer 2 for extracting photo-generated electrons from thelight absorbing layer, a porous insulation substrate 4, and a counterelectrode including a second conducting layer 3 arranged on the oppositeside of the porous insulation substrate 4. The light absorbing layer 1may include a porous metal oxide with dye deposited on metal oxideparticles. The porous insulation substrate 4 is, for example, made of aglass fibres. The first porous conducting layer 2 is a layer of a porousconductive material deposited on one side of the porous insulationsubstrate 4. The second conducting layer 3 is a layer of a porousconductive material deposited on the other side of the porous insulationsubstrate 4. The first and second conducting layers are, for example,printed on the porous insulation substrate. In order to print theconducting layers onto the porous substrate and to handle the poroussubstrate with the printed layers during production, the poroussubstrate must have a certain mechanical stability. The mechanicalstability is normally achieved by controlling the thickness of thesubstrate. The porous insulation substrate is electrically insulating.Both conducting layers 2, 3 comprises particles that are large enough tonot penetrate the pores of the porous substrate. The porous insulationsubstrate 4 serves the function of separating the conducting layersphysically and electrically in order to avoid direct electrical shortcircuit between the conducting layers 2, 3. Further, to allow the firstand second conducting layers 2, 3 to be printed on the porous substrate,the porous substrate should be suitable for printing.

The solar cell in FIG. 1a is infiltrated with an electrically conductingmedium 5 in the pores of the light absorbing layer, in the pores of thefirst and second conducting layers, and in the pores of the poroussubstrate. The conducting medium forms a continuous layer inside thepores of the conducting layers, and between the conducting layers insidethe pores of the porous insulation substrate thereby enabling transportof electrical charge between the counter electrode and the workingelectrode including the light absorbing layer 1. The first porousconducting layer extracts the electrons from the light absorbing layerand transports the electrons to an external electrical circuit connectedto the counter electrode (not shown in FIG. 1). The counter electrode isused to transfer the electrons to the conducting medium. The conductingmedium transfer electrons back to the light absorbing layer therebycompleting the electrical circuit.

Depending on the nature of the conducting medium, either ions orelectrons and holes can be transported between the counter electrode andthe working electrode.

Electrolytes in dye-sensitized solar cells are normally classified asliquid electrolytes, quasi-solid-state electrolytes or solid-stateelectrolytes. The electrolytes can be in the form of a liquid, gel or insolid state. There are a large number of electrolytes of either typeknown in literature, see for example Chemicals Reviews, Jan. 28, 2015,“Electrolytes in Dye-Sensitized Solar Cells”. The electrolytes are anexpensive component of the Dye-Sensitized Solar Cells. The counterelectrode is normally equipped with a catalytic substance 3′ that servesthe purpose of facilitating the transfer of electrons to theelectrolyte.

The conducting medium exhibits a certain electrical resistance totransport charges. The electrical resistance increases with the chargetransport distance. Therefore, when electrical charge is transportedbetween the counter electrode and the light absorbing layer, there willalways be a certain electrical resistive loss in the conducting medium.By making the porous substrate thinner, the resistive losses can bereduced. However, when the porous substrate becomes thinner it alsobecomes more mechanically fragile.

FIG. 1b shows another prior art example of a dye sensitized solar cell,as described in WO2014/184379. This solar cell differs from the solarcell shown in FIG. 1a in that conducting particles forming a conductingnetwork 6 through the insulating material has been inserted in theporous insulating substrate 4. The particles form one or moreelectrically conducting paths through the insulating material of theinsulating substrate 4. Due to the conducting network 6 in theinsulating substrate 4, the distance between the counter electrode andthe light absorbing layer 1 does no longer depend on the thickness ofthe porous substrate 4. Thus, the thickness of the insulating part canbe reduced, and by that the distance between the counter electrode andthe light absorbing layer can be reduced. Accordingly, the resistivelosses in the conducting medium is reduced. Due to the fact that thedistance between the counter electrode and the light absorbing layerdoes no longer depend on the thickness of the whole porous substrate butonly on the insulating part, it is also possible to use a substrate thatis thick enough for safe mechanical handling.

Certain conducting media, like copper and cobalt complex electrolytes,can have very low electrical conductivity resulting in very largeelectrical resistive losses. The low electrical conductivity originatesfrom the fact that the electrolytes have large ions with low diffusionrate. When a liquid electrolyte is to transport charges, thetransporting particles move with Brownian motion; i.e. they moverandomly due to collisions with fast-moving atoms or molecules in theliquid. Copper and cobalt have relatively large ions that are slowmoving and thus have low conductivity. The efficiency of using suchelectrolytes is greatly improved by the above solution.

Another type of solar cell based on disposing a light absorbing layer ontop of a porous conducting layer, a porous insulating layer and acounter electrode is described in the co-pending applicationWO/SE2017/050016. The light absorbing layer comprises grains of forexample doped Si. A polymer charge conductor covers the grains of thelight absorbing layer and extends through the conducting layer andinsulating layer to the counter electrode.

A disadvantage that comes with printing a conducting layer onto a poroussubstrate is that the substrate has to have a thickness that supportsthe process. Further handling of the printed structure during themanufacturing, like conveying or turning sheets or rolls or heattreating or stapling the sheets or rolls require the structure to have acertain mechanical stability. This is achieved by having a certainthickness of the porous substrate.

In order to complete the building of the solar cell, a conducting mediumis disposed into the light absorbing layer, the conducting layer and theporous layer down to the counter electrode. The conducting medium is anexpensive part of the solar cell.

SUMMARY

An aspect of the present disclosure is to provide a solution, whichseeks to mitigate, alleviate, or eliminate one or more of the above andbelow identified deficiencies in the art and disadvantages singly or inany combination. The present disclosure proposes a device and a methodfor minimizing the use of conducting medium in a solar cell.

More specifically, the disclosure provides for a device and a method forminimizing the use of conducting medium in solar cells by using anoverlapping region of conducting medium and conducting and catalyticparticles in the substrate without filling the whole substrate andcounter electrode with conducting medium.

This aspect is achieved by the device and the method as defined in theindependent claims.

According to some aspects of the disclosure, a solar cell is provided.The solar cell comprises a working electrode including a porous lightabsorbing layer, a first porous conducting layer for extractingphoto-generated electrons from the light absorbing layer, wherein thelight absorbing layer is arranged on top of the first porous conductinglayer, a counter electrode including a second conducting layer, a poroussubstrate disposed between the first and second conducting layers,wherein the porous substrate comprises a conducting portion inelectrical contact with the second conducting layer and an insulatingportion disposed between the first porous conducting layer and theconducting portion, and a conducting medium for transporting chargesbetween the conducting portion and the light absorbing layer. Theconducting medium is located in the light absorbing layer, in the firstporous conducting layer, and partly in the porous substrate so that theinsulating portion of the porous substrate comprises the conductingmedium and a first part of the conducting portion that abuts against theinsulating portion comprises the conducting medium and a second part ofthe conducting portion that abuts against the second conducting layer isfree of conducting medium. In other words, the porous substrate ispartially filled with conducting medium such that there are threeregions in the porous substrate; one insulating portion with conductingmedium, one conducting portion with conducting medium and one conductingportion without conducting medium. In this way, the use of conductingmedium can be minimized. This saves a lot of cost, especially in bigscale production, and can also enable the use of more expensiveconducting mediums for better efficiency without significantlyincreasing the costs. Also, for the use of liquid conducting mediums,the risk of leakage can be lowered when smaller amounts of the liquid isused.

Due to the conducting portion in the porous substrate, the insulateddistance between the counter electrode, i.e. the second conductinglayer, and the light absorbing layer does not depend on the totalthickness of the porous substrate. In other words, even when using athick porous substrate, the thickness of the insulating portion 4 b canbe reduced, and by that, the distance between the counter electrode 3and the light absorbing layer 1 can be reduced. Accordingly, theresistive losses in the conducting medium is reduced. Due to the factthat the effective distance for transferring charges between the counterelectrode and the light absorbing layer does not depend on the thicknessof the porous substrate, it is also possible to use a substrate that isthick enough for safe mechanical handling. By also limiting the presenceof the conducting medium to the insulating portion and to the first partof the conducting medium, the amount of used conducting medium isminimized. This makes it possible to have a substrate thick enough forsafe mechanical handling and lower the cost of materials since the wholesubstrate does not need to be filled with conducting medium.

According to some aspects, the conducting medium is located in pores ofthe light absorbing layer, in pores of the first porous conductinglayer, in pores of the insulating portion of the porous substrate and inpores of the first part of the conducting portion. When the conductingmedium is located in the pores of a porous material it is possible forthe conducting medium to form a continuous chain, such that theconducting medium can efficiently transport charges between theconducting portion and the light absorbing layer.

The conducting medium is, for example, a conventional I⁻/I⁻ ₃electrolyte or a similar electrolyte, or a Cu⁻/Co⁻ complex electrolyte.Solid state transition metal based complexes or organic polymer holeconductors are known conducting mediums.

According to some aspects, the conducting portion comprises catalyticelements. The catalytic elements assist in the transfer of chargesbetween the conducting portion and the conducting medium.

According to some aspects, the porous substrate comprises a porousinsulating material and the conducting portion comprises conducting andcatalytic particles accommodated in the pores and forming a conductingnetwork through the insulating material and wherein the conductingmedium is in electrical and catalytic contact with the conductingnetwork in the first part of the conducting portion. Thus, in the partof the porous substrate where the conducting medium and the conductingand catalytic particles overlap, in the first part, they are bothpresent in the pores of the porous substrate. This will give goodelectrical contact between the two.

According to some aspects, the distance between the light absorbinglayer and the first part is between 0.2 μm and 60 μm, and preferablebetween 0.8 and 50 μm. In other words, the conducting medium willtransfer charges the maximum distance of 60 μm or preferably 50 μm.

According to some aspects, the thickness of the conducting portion isless than 1 mm, and preferably less than 100 μm. Due to the fact thatthe conducting portion is thin, the demand on the conductivity of theconducting portion is rather low, and lower than the demand on theconductivity of the first and second conducting layers.

According to some aspects, the thickness of the insulating portion isbetween 0.1 μm and 40 μm, and preferably between 0.5 μm and 20 μm. Thus,the electrical resistive losses in the conducting medium are reduced andstill short circuit is avoided between the first and third conductinglayer.

According to some aspects, the thickness of the first porous conductinglayer is between 0.1 μm and 40 μm, and preferably between 0.3 and 20 μm.The thickness of the first porous conducting layer is advantageouslykept thin in order to have a short distance between the light absorbinglayer and the third conducting layer and the counter electrode.

According to some aspects, the thickness of the first part of theconducting portion, is smaller than the thickness of the second part ofthe conducting portion. In other words, the overlapping part, which isboth conducting and comprises conducting medium, is smaller than thepart which does not comprise conducting medium according to someaspects. The overlapping region only needs to be thick enough to allowfor electrical contact between the conducting portion and the conductingmedium. The thinner the overlapping part, i.e. the first part, is, theless conducting medium can be used. It should be noted that, the limitof where the conducting medium is located in the porous substrate, thatis, the line between the first and the second part of the conductingportion, is not necessarily a straight line.

According to some aspects, the thickness of the porous substrate isbetween 10 μm and 1 mm. Such a layer provides good mechanical strengthto the solar cell.

According to some aspects, the insulating portion (4 b) is an integralpart of the porous substrate (4).

According to some aspects, the conducting medium comprises copper ions.Copper ions, i.e. Cu²⁺, Cu⁺, is a non-toxic conducting medium. The useof copper as conducting medium has been shown to give a very highresulting photo voltage.

According to some aspects, the average pore size of the porous substrateis larger than the average pore size of the first porous conductinglayer, and wherein the average pore size of the first conducing layer islarger than the average pore size of the light absorbing layer. This isadvantageous in the production of the solar cell. When using pores thatare smaller on top and then larger and larger further down the solarcell, capillary action can be utilized. When dispensing conductingmedium in a liquid or gel form on top of the light absorbing layer, theconducting medium does not flow down to the bottom of the solar cell butis kept in the top layer by the capillary action until the top layer isfilled. This is more thoroughly explained in the detailed descriptionwhen discussing the method for producing the solar cell.

According to some aspects, examples of conducting and catalyticparticles comprises one or more of: PEDOT, carbon, platinum, titanium,titanium alloys, nickel, nickel alloys, carbon based materials,conducting oxides, conducting nitrides, conducting carbides andconducting silicides, platinized FTO, ATO, ITO, carbon black, graphene,or carbon nanotubes. The conducting and catalytic particles comprise forexample a conducting core with a catalytic shell or coating. Anotheroption is to use particles having a low activation energy and that areboth conducting and catalytic such as carbon nanotubes, metal carbides,metal nitrides and metal silicides.

According to some aspects, the solar cell is a dye-sensitized solarcell. The light absorbing element is then a dye as explained in thebackground. Conventional dyes known in the art can be used. A dye ischosen to give good efficiency of the solar cell, especially incombination with a copper based conducting medium. The dye can forexample be triarylamine organic dye comprising any of, or a mixture of,dye in the class Donor-π bridge-Acceptor (D-π-A) and in the classDonor-Acceptor-π bridge-Acceptor (D-A-π-A).

Other types of light absorbing elements like doped Si grains, or grainsof CdTe, CIGS, CIS, GaAs, perovskite can also be applicable.

The limited amount of conducting medium in the solar cell needed byusing the above design can make a saving of conducting medium of up to75%.

According to some aspects of the disclosure, a method for manufacturinga solar cell is provided. The solar cell comprises a first porousconducting layer and a second conducting layer and a porous substratedisposed between the first and second conducting layers. The methodcomprises preparing the porous substrate such that the porous substratecomprises a conducting portion at a first side of the porous substrateand an insulating portion at a second side of the porous substrate,depositing a porous conducting layer on the second side of the poroussubstrate to form the first porous conducting layer, depositing thesecond conducting layer such that the conducting portion is inelectrical contact with the second conducting layer, depositing a poroussemiconducting layer on top of the first porous conducting layer to formthe light absorbing layer and depositing a conducting medium onto thelight absorbing layer, and depositing the conducting medium until theconducting medium has entered the light absorbing layer, the firstporous conducting layer and partly the porous substrate so that theinsulating portion of the porous substrate comprises the conductingmedium and a first part of the conducting portion that abuts against theinsulating portion comprises the conducting medium and a second part ofthe conducting portion that abuts against the second conducting layer isfree of conducting medium. The advantages of the resulting solar cell ispreviously discussed. The method is an effective way of depositingcontacting medium such that it does not fill the whole porous substrate,or more in particular, such that it does not fill the conducting portionof the porous substrate. Another advantage with this method is that itis easy to manufacture the solar cell according to the disclosure.

According to some aspects, preparing the porous substrate comprisesdepositing a blocking agent on a second side of the porous substrate,the porous substrate comprising an insulating material, to form ablocking layer in a portion of the substrate and infiltrating the poroussubstrate from a first side of the substrate with conducting andcatalytic particles having a size smaller than the pore size of thesubstrate to form a conducting portion. This is an efficient method toproduce the porous substrate such that is comprises an insulatingportion and a conducting portion.

According to some aspects, preparing the porous substrate comprises,after depositing the first porous conducting layer and the secondconducting layer, heat treating the substrate to burn off the blockinglayer thus forming the insulating portion. Depending on the blockingagent used, it may be kept in the insulating portion or burned off afterdepositing the first and second conducting layers. Some blocking agentsmay not disturb the function of the solar cell and then they can be leftin the substrate.

According to some aspects, depositing the second conducting layercomprises depositing an ink comprising conductive particles on the firstside of the porous substrate. In other words, the second conductinglayer is printed on the first side.

According to some aspects, depositing the second conducting layercomprises depositing a metal layer on the first side of the poroussubstrate. Thus, the second conducting layer is deposited as a sandwichconstruction.

According to some aspects, the conducting medium is comprised in aliquid or gel. When the conducting medium is comprised in a liquid orgel it may simplify deposition of the contacting medium to the lightabsorbing layer, the first conducting medium, the insulating portion andthe first part of the conducting portion.

According to some aspects, the light absorbing layer, the poroussubstrate and the first porous conducting layer are prepared such thatthe first porous conducting layer has a pore size that is smaller thanthe pore size of the porous substrate and such that the light absorbinglayer has a pore size that is smaller than the pore size of the firstporous conducting layer and wherein the capillary action will preventthe liquid or gel from flowing to the first porous conducting layeruntil the light absorbing layer is saturated and to the porous substrateuntil the first porous conducting layer is saturated and prevent theliquid or gel from flowing to the conducting portion until theinsulating portion is saturated and prevent the liquid or gel fromflowing to the second part of the conducting portion. This method fordepositing the conducting medium uses capillary action to prevent thecontacting medium from running too deep in the porous substrate to savethe amount of conducting medium used.

According to some aspects, the conducting medium is prevented fromentering the second part of the conducting portion by polymerizing theliquid or gel before it reaches the second part. Polymerizing the liquidor gel is an efficient way of controlling where, in the solar cell, theconducting medium is deposited.

According to some aspects, the polymerization is initiated using any oneof, or a combination of: UV-light illumination, heating and atwo-component process. The choice of which one to use depends on thechoice of liquid or gel.

BRIEF DESCRIPTION OF THE DRAWINGS

The present technique will be more readily understood through the studyof the following detailed description of the aspects together with theaccompanying drawings, of which:

FIG. 1a shows an example of a prior art dye sensitized solar cell asdescribed in the background.

FIG. 1b shows another example of a prior art dye sensitized solar cellas described in the background.

FIG. 2 illustrates an example of a dye sensitized solar cell.

FIG. 3 is an illustration of a porous substrate with a conductingportion, an insulating portion and overlap of conductive particles in afirst part of the conducting portion.

FIG. 4 shows an example of production of the porous substrate and firstand second conducting layers according to some aspects of thedisclosure.

FIG. 5 shows an example of production of the porous substrate and thefirst and second conducting layers using a blocking layer.

The figures are not to scale, emphasis instead being placed onillustrating the example aspects.

DETAILED DESCRIPTION

Aspects of the present disclosure will be described more fullyhereinafter with reference to the accompanying drawings. Like numbers inthe drawings refer to like elements throughout.

The terminology used herein is for the purpose of describing particularaspects of the disclosure only, and is not intended to limit theinvention. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms used herein should be interpreted ashaving a meaning that is consistent with their meaning in the context ofthis specification and the relevant art and will not be interpreted inan idealized or overly formal sense unless expressly so defined herein.

FIG. 2 shows an example of a dye-sensitized solar cell according to someaspects of the disclosure. The solar cell is preferably a monolithicdye-sensitized solar cell. A monolithic dye-sensitized solar cell ischaracterized in that all layers are directly or indirectly deposited onone and the same porous substrate.

The solar cell comprises a working electrode including a porous lightabsorbing layer 1 and a first porous conducting layer 2 for extractingphoto-generated electrons from the light absorbing layer. The lightabsorbing layer 1 and the first porous conducting layer 2 are porouslayers. The light absorbing layer 1 of the working electrode may includea porous TiO2 electrode layer deposited onto the first porous conductinglayer 2. The TiO2 electrode layer may comprise TiO2 particles dyed byadsorbing dye molecules on the surface of the TiO2 particles. Accordingto some aspects, the solar cell is a dye-sensitized solar cell. Thelight absorbing element is then a dye as explained in the background.Conventional dyes known in the art can be used. A dye is chosen to givegood efficiency of the solar cell, especially in combination with acopper based conducting medium. The light absorbing layer may alsocomprise silicon, Si, grains or grains of CdTe, CIGS, CIS, GaAs,perovskite can also be applicable. The first porous conducting layer 2comprises conducting particles and has, according to some aspects, asurface layer of TiO2.

The light absorbing layer 1 is arranged on top of the first porousconducting layer 2. The solar cell also comprises a counter electrodeincluding a second conducting layer 3 and a porous substrate 4 disposedbetween the first and second conducting layers 2, 3. The poroussubstrate 4 comprises a conducting portion 4 a in electrical contactwith the second conducting layer 3. An insulating portion 4 b isdisposed between the first porous conducting layer 2 and the conductingportion 4 a. The insulating portion 4 b of the porous substrate preventsshort circuit between the first and second conducting layers because itis electrically insulating. In other words, the insulating portion 4 bof the porous substrate 4 serves the function of separating theconducting layers 2, 3 physically and electrically in order to avoiddirect electronic short circuit between the conducting layers 2, 3. Theconducting portion 4 a forms an extension of the second conducting layer3. The first and second conducting layers 2, 3 are, for example, printedon the porous substrate. To allow the first and second conducting layers2, 3 to be printed on the porous substrate, the porous substrate shouldbe suitable for printing. Both conducting layers 2, 3 consist ofparticles that are large enough to not penetrate the pores of the poroussubstrate. The material forming the conducting layers 2, 3 must have asuitable corrosion resistance as to withstand the environment in thesolar cell, and preferably also be resistant to temperatures above 500°C. in air without losing adequate conductivity. Preferably, theconducting layers 2, 3 are made of a material selected from a groupconsisting of titanium, titanium alloys, nickel, nickel alloys,graphite, and amorphous carbon, or mixtures thereof.

It should be noted that the first and second conducting layers 2, 3 arepositioned on a shadow side of the light absorbing layer 1, i.e. theside opposite the side receiving the light. Thus, the first and secondconducting layers are positioned on the same side of the light absorbinglayer as shown in the figures.

The solar cell also comprises a conducting medium 5 for transportingcharges between the conducting portion 4 a and the light absorbing layer1. The conducting medium is located in the light absorbing layer 1, inthe first porous conducting layer 2, and partly in the porous substrate4 so that the insulating portion 4 b of the porous substrate comprisesthe conducting medium and a first part 4 a′ of the conducting portion 4a that abuts against the insulating portion comprises the conductingmedium and a second part 4 a″ of the conducting portion that abutsagainst the second conducting layer is free of conducting medium. Inother words, the porous substrate is partially filled with conductingmedium such that there are three regions in the porous substrate; oneinsulating portion with conducting medium, one conducting portion withconducting medium and one conducting portion without conducting medium.In this way, the use of conducting medium can be minimized. FIG. 3 is anillustration of the porous substrate 4, with the three regions 4 a′, 4a″ and 4 b. The conducting medium 5 is in electrical contact with theconducting portion 4 a, in the figure illustrated as conductingparticles in a network, such that it can transfer charges from thesecond conducting layer 3, via the conducting portion 4 a of the poroussubstrate 4, to the light absorbing layer 1. This is cost saving,especially in big scale production, and can also enable the use of moreexpensive conducting mediums for better efficiency without significantlyincreasing the costs. Also, for the use of liquid conducting mediums,the risk of leakage can be lowered when smaller amounts of the liquid isused. It should be noted that “free of conducting medium” means thatthere is little enough conducting medium such that the conducting mediumin itself cannot transfer charges. Preferably, the second part 4 a″ doesnot contain any conducting medium, but in the manufacturing process, itwill be very difficult to prevent some conducting medium from enteringthe second part. It should be further noted that the second conductinglayer is inherently also free of conducting medium since it is locatedbelow the second part 4 a″.

Due to the conducting portion 4 a in the porous substrate 4, theinsulated distance between the counter electrode, i.e. the secondconducting layer 3, and the light absorbing layer 1 does not depend onthe total thickness of the porous substrate 4. In other words, even whenusing a thick porous substrate, the thickness of the insulating portion4 b can be reduced, and by that, the distance between the counterelectrode 3 and the light absorbing layer 1 can be reduced. Accordingly,the resistive losses in the conducting medium 5 is reduced. Due to thefact that the distance for the charges to travel between the secondconducting layer 3 and the light absorbing layer 1 does not depend onthe thickness of the porous substrate 4, it is possible to use asubstrate that is thick enough for safe mechanical handling. By alsolimiting the presence of the conducting medium to the insulating portion4 b and to the first part 4 a′ of the conducting portion 4 a, the amountof used conducting medium 5 is minimized. The limited amount ofconducting medium in the solar cell needed by using the above design canmake a saving of conducting medium of up to 75%. This makes it even morepossible to have a substrate thick enough for safe mechanical handlingsince the whole substrate does not need to be filled with conductingmedium which can be expensive. Furthermore, the effectiveness of thesolar cell will not be as sensitive to the choice of conducting medium.For example, copper ions, which are easily obtainable but is anexpensive, large and slow ion can be used more advantageously thanbefore. Due to the fact that the conducting medium 5 does not fill thewhole porous substrate 4 but only such that it overlaps with, and is inelectrical contact with, the conducting portion 4 a′, for example copperions can be used advantageously. The porous substrate must allow forfast transport of ions or holes between the electrodes. In order todistribute the conducting medium, the substrate must have sufficientlyhigh porosity (pore volume fraction) and low tortuosity.

When the conducting medium 5 is located in the pores of a porousmaterial, the conducting medium forms a continuous chain, such that theconducting medium efficiently can transport charges between theconducting portion 4 a and the light absorbing layer 1. It should benoted that the conducting medium 5 is illustrated as random dots in FIG.2. However, it is merely an illustration of where the conducting mediumis present, not how the particles are actually positioned. Thus,according to some aspects, the light absorbing layer 1 and the firstporous conducting layer 2 are porous, and the conducting medium 5 islocated in pores of the light absorbing layer 1, in pores of the firstporous conducting layer 2, in pores of the insulating portion 4 b of theporous substrate 4 and in pores of the first part 4 a′ of the conductingportion 4 a. Important features of the finished solar cell product arethat the distance to travel for the charges between the secondconducting layer 3 and the light absorbing layer 1 is short and that theproduct is mechanically strong enough for handling.

The first porous conducting layer 2 and the porous substrate 4 areporous to allow the conducting medium to penetrate through theconducting layers when the conducting medium is applied after the layershave been formed. The conducting medium 5 is for example a solid-statehole conductor, or an ionic liquid based electrolyte or a cobalt complexbased electrolyte. However, the conducting medium can be any suitableconducting medium. The conducting medium can be a liquid, a gel, or asolid material such as a semiconductor. Examples of electrolytes areliquid electrolytes (such as those based on the I−/I3−, redox couple orcobalt complexes as redox couple), gel electrolytes, dry polymerelectrolytes and solid ceramic electrolytes. Examples of semiconductorsare inorganic semiconductors, such as CuSCN or CuI, and organicsemiconductors, such as, e.g., Spiro-OMeTAD.

The conducting medium 5 needs to penetrate through the first porousconducting layer 2 to be able to deliver the electrons to the lightabsorbing layer. Thus, the first porous conducting layer needs to havesufficiently high porosity (pore volume fraction) and/or low tortuosity.This can be achieved with canals through the layer, with big grains inthe layer, with monodisperse particles and/or pore forming agents.

FIG. 4 is an illustration of a method for manufacturing the solar cell.As described above, the solar cell comprises the first porous conductinglayer 2 and the second conducting layer 3 and the porous substrate 4disposed between the first and second conducting layers. The methodcomprises preparing S1 the porous substrate 4 such that the poroussubstrate comprises the conducting portion 4 a at a first side 41 of theporous substrate and the insulating portion 4 b at a second side 42 ofthe porous substrate, as shown in the figure as S1. A porous conductinglayer is deposited S2 on the second side 42 of the porous substrate toform the first porous conducting layer 2. The second conducting layer 3is deposited S3 such that the conducting portion 4 a is in electricalcontact with the second conducting layer and a porous semiconductinglayer is deposited S4 on top of the first porous conducting layer 2 toform the light absorbing layer 1. Details of example ways to deposit thelayers will be described further down. This structure has severaladvantages such as ease of large-scale manufacturing and providing awell-defined and constant distance between the second conducting layerand the light absorbing layer, when deposited on top of the first porousconducting layer.

The first side 41 is the bottom side and the second side 42 is the topside of the porous substrate 4 as shown in FIG. 3. As shown in FIG. 3,the conducting portion 4 a is located in the lower part of the poroussubstrate 4 and the insulating portion 4 b is located in the upper partof the porous substrate 4. Thus, the porous substrate 4 comprises twoparts, the conducting portion 4 a and the insulating portion 4 b; theconducting portion 4 a is at the first side 41 of the porous substrate 4and the insulating portion 4 b is at the second side 42 of the poroussubstrate 4. In other words, the conducting portion 4 a is located at aside of the porous substrate 4 associated with the first side 41 and theinsulating portion 4 b is located at a side of the porous substrate 4associated with the second side 42.

The porous substrate 4 is, for example, made of microfibers. Amicrofiber is a fibre having a diameter less than 10 μm and lengthlarger than 1 nm. Suitably, the porous substrate comprises wovenmicrofibers. Ceramic microfibers are fibres made of a refractory andinert material, SiO₂, Al₂O₃ and aluminosilicate. The microfibers mayalso be glass microfibers. Organic microfibers are fibres made oforganic materials such as polymers such as, e.g., polycaprolactone, PET,PEO etc, or cellulose such as, e.g., nanocellulose (MFC) or wood pulp.

The porous substrate 4 may comprise woven microfibers and non-wovenmicrofibers disposed on the woven microfibers.

The conducting medium 5 is deposited S4 onto the light absorbing layer1, and the conducting medium is deposited until the conducting mediumhas entered the light absorbing layer 1, the first porous conductinglayer 2 and partly the porous substrate 4 so that the insulating portion4 b of the porous substrate comprises the conducting medium and a firstpart 4 a′ of the conducting portion that abuts against the insulatingportion 4 b comprises the conducting medium and a second part 4 a″ ofthe conducting portion that abuts against the second conducting layer isfree of conducting medium. The advantages of the resulting solar cell ispreviously discussed. The method is an effective way of depositingconducting medium 5 such that it does not fill the whole poroussubstrate 4, or more in particular, such that it does not fill the wholeconducting portion 4 a of the porous substrate. In other words, theconducting portion 4 a is partially filled with conducting medium 5 suchthat the conducting medium is in electrical contact with the conductingportion. Another advantage with this method is that it is easy tomanufacture the solar cell according to the disclosure. It should benoted that if the depositing of the conducting medium is continued afterreaching the first part, it will continue to flow to the second part.The amount of deposited conducting media will therefore be important.

The conducting medium is for example a conventional I⁻/I⁻ ₃ electrolyteor a similar electrolyte, or a Cu or Co complex based electrolyte. Solidstate transition metal based complexes or organic polymer holeconductors are known conducting mediums. According to some aspects, theconducting medium is PEDOT.

As previously discussed, the first and second conducting layers 2, 3can, for example, be deposited by printing. The first porous conductinglayer 2 may alternatively be formed by evaporation or sputtering of atitanium layer onto the porous substrate, or any other method fordepositing a thin layer of titanium onto the porous substrate 4. Thesecond conducting layer 3 is for example deposited S3 by depositing S3 aan ink comprising conductive particles on the first side 41 of theporous substrate 4. In other words, the second conducting layer isprinted on the first side 41. Another alternative is that depositing S3the second conducting layer 3 comprises depositing S3 b a metal layer onthe first side 41 of the porous substrate 4. Thus, the second conductinglayer is deposited as a sandwich construction.

The light absorbing layer 1 is deposited onto the first porousconducting layer 2. The light absorbing layer is, for example, formed bydepositing a porous TiO2 layer onto the first porous conducting layerand thereafter adsorb a dye onto the TiO2 layer in the case that thesolar cell is a dye-sensitized solar cell. The conducting medium 5 isdeposited onto the light absorbing layer 1 before depositing onto thefirst porous conducting layer 2 such that the conducting medium 5 firstfills the light absorbing layer 1 and then continues to fill the firstconducting medium 2 according to above. The solar cell comprises a lightabsorbing layer 1 and the depositing of the conducting medium 5 is doneonto the light absorbing layer 1 and then onto the first porousconducting layer 2 from the light absorbing layer and so on. Hence, theconducting medium 5 is located in the light absorbing layer 1, in thefirst porous conducting layer 2, in the insulating portion 4 b and inthe first part 4 a′ of the conducting portion 4 a such that theconducting medium 5 forms a continuous conducting path between the firstpart and the light absorbing layer.

One way of controlling how many layers the conducting medium penetrates,that is, controlling the conducting medium 5 such that it does not enterthe second part 4 a″ of the conducting portion, is to deposit apredetermined amount of conducting medium 5 onto the first porousconducting layer 2 or the light absorbing layer 1. The pores of thelight absorbing layer 1 should be as filled with conducting medium aspossible to maximise the efficiency of the solar cell. According to someaspects, the conducting medium 5 is deposited until there is an adequateelectrical connection between the first part 4 a′ and the lightabsorbing layer 1. In other words, the conducting medium 5 is depositeduntil there is an overlap between the conducting medium 5 and theconducting portion 4 a of the porous substrate 4.

Capillary action (sometimes called capillarity, capillary motion, orwicking) is the ability of a liquid, or solvent, to flow in narrowspaces without the assistance of, or even in opposition to, externalforces like gravity. According to some aspects, the average pore size ofthe porous substrate 4 is larger than the average pore size of the firstporous conducting layer 2, and wherein the average pore size of thefirst conducing layer 2 is larger than the average pore size of thelight absorbing layer 1. This is advantageous in the production of thesolar cell. When using pores that are smaller on top and then larger andlarger further down the solar cell, capillary action can be utilized.When dispensing conducting medium in a liquid or gel form on top of thelight absorbing layer or the first porous conducting layer, depending onthe method, the conducting medium does not flow down to the bottom ofthe solar cell but is kept in the top layer by the capillary actionuntil the top layer is filled.

As previously discussed, FIG. 3 is an illustration of an example of theporous substrate 4, with the three regions 4 a′, 4 a″ and 4 b. Accordingto some aspects, the conducting portion comprises catalytic elements.The catalytic elements assist in the transfer of charges between theconducting portion and the conducting medium. It can be seen in thefigure that the conducting portion 4 a comprises a network of particles.Those particles are conducting particles and according to some aspects,the porous substrate 4 comprises a porous insulating material and theconducting portion 4 a comprises conducting and catalytic particlesaccommodated in the pores and forming a conducting network 6 through theinsulating material and wherein the conducting medium is in electricaland catalytic contact with the conducting network in the first part ofthe conducting portion. Thus, in the part of the porous substrate 4where the conducting medium 5 and the conducting and catalytic particlesoverlap, in the first part 4 a′, they are both present in the pores ofthe porous substrate. This will give good electrical contact between thetwo. In the figure, the porous substrate 4 comprises a conductingportion 4 a including conducting particles forming a conducting network6 in the insulating material of the porous substrate, and an insulatingportion 4 b without any conducting particles and forming a porousinsulating layer. The insulating portion 4 b is here formed as anintegral part of the porous substrate 4.

The conducting network 6 is in direct physical and electrical contactwith the second conducting layer 3 of the counter electrode and willtherefore significantly increase the conductive surface area of thecounter electrode. The conducting surface area serves the function oftransferring electrons or holes from the counter electrode to theconducting network. The conducting network in the porous substrate andthe thus increased conductive surface area of the second conductinglayer decrease the charge transfer resistance between the conductingmedium 5 and the conducting network 6. Additionally, since theconducting portion 4 a forms a conducting network extending through theinsulating material of the porous substrate, the distance between thelight absorbing layer 1 and the conducting portion 4 a is shorter thanthe distance between the light absorbing layer 1 and the secondconducting layer 3. The conducting particles are smaller than theaverage pore size of the porous layer 4 in order to be infiltratedeffectively.

The conducting particles in the conducting portion 4 a may consist ofthe same material as is used in the second conducting layer 3. It isalso possible to use other types of particles such as carbon basedmaterials (graphite, carbon black, CNT, graphene, etc). It is alsopossible to use other types of particles such as conducting oxides (ITO,FTO, ATO etc) or carbides, nitrides or silicides. According to someaspects, the conducting and catalytic particles comprises one or moreof: PEDOT, carbon, platinum, titanium, titanium alloys, nickel, nickelalloys, carbon based materials, conducting oxides, conducting nitrides,conducting carbides, conducting silicides, platinized FTO, ATO, ITO,carbon black, graphene, and carbon nanotubes. The conducting andcatalytic particles comprise for example a conducting core with acatalytic shell or coating. The conducting core can be made of metal,metal alloy, metal oxide, or other conducting materials. Another optionis to use particles having a low activation energy and that are bothconducting and catalytic such as carbon nanotubes, metal carbides, metalnitrides and metal silicides.

The conducting medium 5 comprises for example ions and according to someaspects, the conducting medium 5 comprises copper ions. Copper ions,i.e. Cu²⁺, Cu⁺, is a non-toxic conducting medium and has been shown togive good efficiency, especially in dye-sensitized solar cells.

The ions are free moving ions for transferring charges between thecounter electrode and the light absorbing layer. Another example of ionsthat may be used as conducting medium is cobalt ions. The conductingmedium may also be a cobalt based electrolyte, a cobalt complex basedelectrolyte or a copper complex based electrolyte. The conducting mediumcomprises according to some aspects ligands, such as phenanthrolines.The most common used ion combination used as electrolyte is the I⁻/I₃ ⁻.

Depending on the nature of the conducting medium, either ions orelectrons and holes, can be transported between the counter electrode 3and the working electrode 1. The conducting medium 5 may for example bea solid-state hole conductor. A solid-state hole conductor is, forexample, a semiconductor. An advantage using a hole conductor is that itis a solid material and accordingly the requirement of sealing of thesolar cell is reduced. Examples of semiconductors are inorganicsemiconductors, such as CuSCN or CuI, and organic semiconductors, suchas, e.g., P3HT or Spiro-OMeTAD. According to some aspects, theconducting medium is a solid-state hole conductor, or an ionic liquidbased electrolyte, or a cobalt complex based electrolyte. Semiconductingperovskites, like CH₃NH₃PbI₃, CH₃NH₃PbI_(3-x)Cl_(x) or CH₃NH₃SnI₃ orother suitable perovskites can be used.

The thicknesses of the layers of this disclosure will depend on manyfactors. Efficiency of the solar cell is obviously important, such isalso the mechanical strength of the solar cell; it must be possible tohandle both during production and as a finished product withoutbreaking. But the required mechanical strength may vary depending on howand where the solar cell will be used. The efficiency may also besacrificed in order to produce a cheaper solar cell and also dependingon the intended use of the solar cell. Method of manufacturing will alsoinfluence which thicknesses are possible. Therefore, the thicknesses ofthe layers may vary. According to some aspects, the thickness of thefirst part 4 a′ of the conducting portion 4 a is smaller than thethickness of the second part 4 a″ of the conducting portion. In otherwords, the overlapping part, which is both conducting and comprisesconducting medium 5, is smaller than the part which does not compriseconducting medium. The overlapping region only needs to be thick enoughto allow for electrical contact between the conducting portion and theconducting medium. The thinner the overlapping part, i.e. the firstpart, is, the less conducting medium 5 can be used. The thickness of thesecond part 4 a″ of the conducting portion depends on the desiredmechanical strength of the packet of layers to be handled duringmanufacturing and the resulting solar cell.

It should be noted that, depending on the method of manufacture, thelimit of where the conducting medium is located in the porous substrate,that is, the line between the first and the second part of theconducting portion, is not necessarily a straight line. It should benoted that by using the method described above, the line will mostlikely have an irregular shape where the conducting medium has enteredthe porous substrate at different depths.

As explained, some can be said about the thicknesses of the differentlayers but the skilled person realizes that the thicknesses will dependtoo much of the implementation and manufacturing process of the solarcell for providing exact measurements. According to some aspects, thedistance between the light absorbing layer 1 and the first part 4 a′ isbetween 0.2 μm and 60 μm, and preferable between 0.8 and 50 μm. In otherwords, the conducting medium will transfer charges the maximum distanceof 60 μm or preferably 50 μm. According to some aspects, the thicknessof the conducting portion 4 a is less than 1 mm, and preferably lessthan 100 μm. Due to the fact that the conducting portion is thin, thedemand on the conductivity of the conducting portion is rather low, andlower than the demand on the conductivity of the first and secondconducting layers. According to some aspects, the thickness of theinsulating portion 4 b is between 0.1 μm and 40 μm, and preferablybetween 0.5 μm and 20 μm. Thus, the electrical resistive losses in theconducting medium are reduced and still short circuit is avoided betweenthe first and third conducting layer. According to some aspects, thethickness of the first porous conducting layer 2 is between 0.1 μm and40 μm, and preferably between 0.3 and 20 μm. The thickness of the firstporous conducting layer is advantageously kept thin in order to have ashort distance between the light absorbing layer and the thirdconducting layer and the counter electrode.

According to some aspects, the thickness of the porous substrate 4 isbetween 10 μm and 1 mm. Such a layer provides good mechanical strengthto the structure of layers during production and to the resulting solarcell.

One way to prepare the porous substrate is illustrated in FIG. 5.According to some aspects, preparing S1 the porous substrate 4 comprisesdepositing S11 a blocking agent on a second side 42 of the poroussubstrate 4, the porous substrate comprising an insulating material, toform a blocking layer 7 in a portion 4 b of the substrate, andinfiltrating S12 the porous substrate from a first side 41 of thesubstrate with conducting and catalytic particles having a size smallerthan the pore size of the substrate to form a conducting portion 4 a.This is an efficient method to produce the porous substrate such that iscomprises an insulating portion 4 b and a conducting portion 4 a. Usingthis method forms the network of conducting particles 6, which has beenpreviously discussed. The blocking agent is either a material, such asfibres, that does not affect the function of the solar cell, and canthus be left there, or it is burned off after depositing the first andsecond conducting layers. Therefore, according to some aspects,preparing S1 the porous substrate 4 comprises, after depositing S2, S3the first porous conducting layer 2 and the second conducting layer 3,heat treating S13 the substrate to burn off the blocking layer thusforming the insulating portion 4 b. Again, depending on the blockingagent used, it may be kept in the insulating portion or burned off afterdepositing the first and second conducting layers. Some blocking agentsmay not disturb the function of the solar cell and then they can be leftin the substrate.

Some of the layers may require heat treatment for sintering them. Thelight absorbing layer 1 and the conducting layers 2, 3 may requiresintering. The conducting layers 2, 3 may be sintered in the same heattreatment as the light absorbing layer or earlier. When the heattreatment is performed will depend on the material choices. Someconducting media may be sensitive to heat treatment and if such a mediais used, the heat treatment should be performed before depositing theconducting medium.

As previously discussed, capillary action may be used in producing thesolar cells. According to some aspects, the light absorbing layer 1, theporous substrate 4 and the first porous conducting layer 2 are preparedsuch that the first porous conducting layer 2 has a pore size that issmaller than the pore size of the porous substrate 4 and such that thelight absorbing layer 1 has a pore size that is smaller than the poresize of the first porous conducting layer 2 and wherein the capillaryaction will prevent the liquid or gel from flowing to the first porousconducting layer until the light absorbing layer is saturated and to theporous substrate until the first porous conducting layer is saturatedand prevent the liquid or gel from flowing to the conducting portion 4 auntil the insulating portion 4 b is saturated and prevent the liquid orgel from flowing to the second part 4 a″ of the conducting portion Thismethod for depositing the conducting medium 5 uses capillary action toprevent the contacting medium from running too deep in the poroussubstrate 4 to save the amount of conducting medium used.

There may be several ways to prevent the conducting medium 5 fromentering the second part 4 a″ of the conducting portion 4 a. One way theconducting medium may be prevented from entering the second part 4 a″ ofthe conducting portion 4 a is by polymerizing the liquid or gel beforeit reaches the second part. Polymerizing the liquid or gel is anefficient way of controlling where, in the solar cell, the conductingmedium is located. According to some aspects, the polymerization isinitiated using any one of, or a combination of: UV-light illumination,heating and a two-component process. The choice of which one to usedepends on the choice of liquid or gel. Another way of stopping theconducting medium from flowing into the second part 4 a″ is to use aliquid or gel that hardens by cooling it or that hardens by evaporationor polymerizing of parts or all of the gel or liquid matrix. The processcan be quickened by heating.

When the conducting medium 5 is comprised in a liquid or gel it maysimplify deposition of the contacting medium to the light absorbinglayer, the first porous conducting layer, the insulating portion and thefirst part of the conducting portion. The conducting medium is forexample comprised in a liquid or gel. The liquid or gel is for exampleacetonitrile, CH3CN, ionic liquid, ionic gel, solvent with dissolvedions or a liquid that changes to gel depending on temperature. Accordingto some aspects, the liquid or gel is dried after deposition such thations of the conducting medium are dried into the layers and forming aconducting chain of conducting particles.

Above, some examples of dyes that can be used in the light absorbinglayer have been discussed in the case that the solar cell is adye-sensitized solar cell. There are many dyes that may be used andaccording to some aspects, the dye comprises triarylamine organic dyecomprising any of, or a mixture of, dye in the class Donor-πbridge-Acceptor (D-π-A) and in the class Donor-Acceptor-πbridge-Acceptor (D-A-π-A). Such dyes give good efficiency of the solarcell, especially in combination with a copper based conducting medium.

Of the first-class photosensitizer are, for example, substituted(diphenylaminophenyl)-thiophene-2-cyanoacrylic acids or substituted(diphenylaminophenyl)cyclopenta-dithiophene-2-cyanoacrylic acids.

Of the second class are, for example, substituted(((diphenylaminophenyl)benzothia-diazolyl)-cyclopentadithiophenyl)aryl/heteroaryl-2-cyanoacrylicacids or(((diphenyl-aminophenyl)-cyclopentadithiophenyl)benzothiadiazolyl)aryl/heteroaryl-2-cyano-acrylicacids.

Examples of sensitizer, i.e. dyes, which may be used are:

-   XY1:    (E)-3-(4-(6-(7-(4-(bis(2′,4′-bis((2-ethylhexyl)oxy)-[1,1′-biphenyl]-4-yl)amino)phenyl)benzo[c][1,2,5]thiadiazol-4-yl)-4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b′]dithiophen-2-yl)phenyl)-2-cyanoacrylic    acid-   XY1b:    (E)-3-(4-(6-(7-(4-(bis(2′,4′-dibutoxy-[1,1′-biphenyl]-4-yl)amino)phenyl)benzo[c][1,2,5]thiadiazol-4-yl)-4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b′]dithiophen-2-yl)phenyl)-2-cyanoacrylic    acid-   Dyenamo blue:    (E)-3-(5-(4-(4-(5-(4-(bis(2′,4′-dibutoxy-[1,1′-biphenyl]-4-yl)amino)phenyl)thiophen-2-yl)-2,5-bis(2-ethylhexyl)-3,6-dioxo-2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrol-1-yl)phenyl)furan-2-yl)-2-cyanoacrylic    acid-   Dyenamo blue 2016:    (E)-3-(5-(4-(4-(5-(4-(bis(2′,4′-dibutoxy-[1,1′-biphenyl]-4-yl)amino)phenyl)thiophen-2-yl)-2,5-dioctyl-3,6-dioxo-2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrol-1-yl)phenyl)furan-2-yl)-2-cyanoacrylic    acid-   D35:    (E)-3-(5-(4-(bis(2′,4′-dibutoxy-[1,1′-biphenyl]-4-yl)amino)phenyl)thiophen-2-yl)-2-cyanoacrylic    acid-   D45:    (E)-3-(5-(4-(bis(2′,4′-dimethoxy-[1,1′-biphenyl]-4-yl)amino)phenyl)thiophen-2-yl)-2-cyanoacrylic    acid-   D35CPDT, LEG4:    3-{6-{4-[bis(2′,4′-dibutyloxybiphenyl-4-yl)amino-]phenyl}-4,4-dihexyl-cyclopenta-[2,1-b:3,4-b′]dithiophene-2-yl}-2-cyanoacrylic    acid-   D51:    (E)-3-(6-(4-(bis(2′,4′-dimethoxy-[1,1′-biphenyl]-4-yl)amino)phenyl)-4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b′]dithiophen-2-yl)-2-cyanoacrylic    acid-   Y123:    3-{6-{4-[bis(2′,4′-dihexyloxybiphenyl-4-yl)amino-]phenyl}-4,4-dihexyl-cyclopenta-[2,1-b:3,4-b′]dithiphene-2-yl}-2-cyanoacrylic    acid-   JF419:    E)-3-(6-(4-(bis(5,7-bis(hexyloxy)-9,9-dimethyl-9H-fluoren-2-yl)amino)phenyl)-4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b′]dithiophen-2-yl)-2-cyanoacrylic    acid-   MKA253:    (E)-3-(6-(4-(bis(5,7-dibutoxy-9,9-dimethyl-9H-fluoren-2-yl)amino)phenyl)-4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b′]dithiophen-2-yl)-2-cyanoacrylic    acid-   L0: 4-(diphenylamino)phenylcyanoacrylic acid-   L1: 5-[4-(diphenylamino)phenyl]thiophene-2-cyanoacrylic acid-   L2: 3-(5-(4-(diphenylamino)styryl)thiophen-2-yl)-2-cyanoacrylic acid

In the following, an example of a method for manufacturing a firstexample of a solar cell according to the invention is described. Aporous substrate 4 made of an insulating material is infiltrated withconducting and catalytic particles having a size smaller than the poresize of the substrate to form a conducting portion 4 a of the poroussubstrate. A layer of insulating material is deposited on one side ofthe porous substrate to form an insulating portion 4 b. The insulatingmaterial is, for example, microfibers made of a ceramic or organicmaterial. An ink comprising conductive particles are deposited on theporous insulating portion to form the first porous conducting layer 2,and an ink comprising conductive particles are deposited on an oppositeside of the porous substrate to form the second conducting layer 3. Theinsulating layer is, for example, deposited on the porous substrate byscreen printing, slot die coating, spraying, or wet laying. The porousfirst and second conducting layers are, for example, deposited on theporous substrate by screen printing or any other suitable printingtechnique. A heat treatment may thereafter take place in order to sinterthe first and second conducting layers. A porous semiconducting layer isprinted onto the first porous conducting layer. Thereafter, thestructure comprising the semiconducting layer, the conducting portion,the insulating portion and the first and second conducting layers isheat treated in order to sinter the porous semiconducting layer and, ifpreviously not heat treated, also sintering of the first and secondconducting layers may take place. The semiconducting layer may beinfiltrated by an ink comprising a dye, thus forming the light-absorbinglayer. An ink comprising the conducting medium is deposited so that thelight-absorbing layer, the first porous conducting layer, the insulatinglayer and an upper part 4 a′ of the conducting portion is penetrated bythe conducting medium. The lower part 4 a″ and the second conductinglayer 3 are not penetrated by the conducting medium, thus economizingwith the conducting medium.

In the following, an example of a method for manufacturing a solar cellaccording to the disclosure is described with reference to FIGS. 4 and5. FIGS. 4 and 5 illustrates the deposition sequences in themanufacturing method.

Step 1: A blocking agent is deposited on a second side 42 of a substrate4 made of an insulating material, to form a blocking layer 7 in aninsulating portion 4 b of the substrate 4. The blocking layer isdeposited in order to physically prevent the conducting particles frombeing infiltrated all the way to other side of the substrate. Therefore,the blocking layer 7 prevents direct physical and electrical contactbetween the first porous conducting layer and the conducting particles.The blocking layer may consist of polymers, ceramic particles, polymerfibres, glass fibers, carbon nanotubes (CNT), nanocellulose ormicrofibrillated cellulose (MFC). It is advantageous to use fibers as ablocking agent in the blocking layer. It is advantageous to use fibreswith very small diameter.

Step 2: The porous substrate 4 is infiltrated from a first side 41 ofthe substrate with conducting particles and catalytic particles orparticles being both conductive and catalytic having a size smaller thanthe pore size of the substrate to form a conducting portion 4 a in afirst portion of the substrate.

Step 3: An ink comprising conductive particles is printed on the secondside 42 of the porous substrate 4 to form the first porous conductinglayer 2.

Step 4: An ink comprising conductive particles is printed on the firstside 41 of the porous substrate 4 to form the second conducting layer 3.

Step 5: The structure is heat treated to burn off the blocking layer 10thus forming the insulating portion 4 b and the conducting portion 4 a.

Step 6: A TiO2 electrode layer is deposited onto the first porousconducting layer 2 to form the working electrode, i.e. the lightabsorbing layer 1.

Step 7: The structure is heat treated to sinter the TiO2 electrode. Theconducting layers 2, 3 may be sintered in the same heat treatment stepor in an earlier step.

Step 8: The TiO2 electrode is infiltrated with a dye.

Step 9: A conducting medium is deposited so that the pores of the TiO2layer, i.e. the light absorbing layer 1, the first porous conductinglayer 2, the insulating portion 4 b and the first part 4 a′ of theconducting portion are filled with conducting medium. The second part (4a″) of the conducting portion is kept at a lower temperature, thuspreventing the conducting medium to penetrate down to that part.

The invention is not limited to the above described example and can bevaried within the scope of the claims. As an example, materials used forthe different layers may vary depending on desired efficiency/cost ratioand on availability of different materials. Further, the method formanufacturing a solar cell can be carried out in many different wayswithin the scope of the claims. For example, there are many differentkinds of chemical treatments that can be performed on the differentlayers of the solar cell but such treatments are not relevant to thedescribed invention.

LIST OF REFERENCE NUMBERS

-   1: light absorbing layer-   2: first porous conducting layer-   3: second conducting layer-   3′: catalytic substance-   4: porous substrate-   41: first side-   42: second side-   4 a: conducting portion-   4 a′: first part of the conducting portion-   4 a″: second part of the conducting portion-   4 b: insulating portion-   5: conducting medium-   6: conducting network-   7: blocking layer

The invention claimed is:
 1. A solar cell comprising: a workingelectrode including a porous light absorbing layer, a first porousconducting layer that extracts photo-generated electrons from the lightabsorbing layer, wherein the light absorbing layer is arranged on top ofthe first porous conducting layer, a counter electrode including asecond conducting layer, a porous substrate made of a porous insulatingmaterial and disposed between the first porous conducting layer and thesecond conducting layer, wherein the porous substrate comprises: aconducting portion comprising conducting particles in pores of theporous insulating material and forming a conductive network in theconducting portion that is in electrical contact with the secondconducting layer, and an insulating portion disposed between the firstporous conducting layer and the conducting portion, and a conductingmedium that transports charges between the conducting portion and thelight absorbing layer, wherein the conducting medium is located in thelight absorbing layer, in the first porous conducting layer, and partlyin the porous insulating material of the porous substrate, and whereinthe insulating portion of the porous substrate has the conducting mediumtherein, wherein a first part of the conducting portion that abuts theinsulating portion has the conducting medium therein, and wherein asecond part of the conducting portion that abuts the second conductinglayer, and is between the first part of the conducting portion and thesecond conducting layer, is free of the conducting medium.
 2. The solarcell according to claim 1, wherein the conducting medium is located inpores of the light absorbing layer, in pores of the first porousconducting layer, in pores of the insulating portion of the poroussubstrate and in pores of the first part of the conducting portion. 3.The solar cell according to claim 2, wherein the conducting portioncomprises catalytic elements.
 4. The solar cell according to claim 3,wherein the conducting portion comprises conducting and catalyticparticles in the pores of the porous insulating material to form theconductive network in the insulating material and wherein the conductingmedium is in electrical and catalytic contact with the conductivenetwork in the first part of the conducting portion.
 5. The solar cellaccording to claim 1, wherein a distance between the light absorbinglayer and the first part of the conducting portion is between 0.2 μm and60 μm.
 6. The solar cell according to claim 1, wherein a thickness ofthe conducting portion is less than 1 mm.
 7. The solar cell according toclaim 1, wherein a thickness of the insulating portion is between 0.1 μmand 40 μm.
 8. The solar cell according to claim 1, wherein a thicknessof the first porous conducting layer is between 0.1 μm and 40 μm.
 9. Thesolar cell according to claim 1, wherein a thickness of the first partof the conducting portion is smaller than a thickness of the second partof the conducting portion.
 10. The solar cell according to claim 1,wherein a thickness of the porous substrate is between 10 μm and 1 mm.11. The solar cell according to claim 1, wherein the insulating portionis an integral part of the porous substrate.
 12. The solar cellaccording to claim 1, wherein the conducting medium comprises copperions.
 13. The solar cell according to claim 1, wherein an average poresize of the porous substrate is larger than an average pore size of thefirst porous conducting layer, and wherein the average pore size of thefirst porous conducing layer is larger than an average pore size of thelight absorbing layer.
 14. The solar cell according to claim 4, whereinthe conducting and catalytic particles comprise one or more of: PEDOT,carbon, platinum, titanium, titanium alloys, nickel, nickel alloys,carbon based materials, conducting oxides, conducting nitrides,conducting carbides, conducting silicides, platinized FTO, ATO, ITO,graphene and carbon nanotube particles.